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jmc

counting and probability intermediate

Problem

How many four-digit positive integers have at least one digit that is a 2 or a 3?
Solution
There are 9000 four-digit positive integers. For those without a 2 or 3, the first digit could be one of the seven numbers 1, 4, 5, 6, 7, 8, or 9, and each of the other digits could be one of the eight numbers 0, 1, 4, 5, 6, 7, 8, or 9. So there are four-digit numbers with at least one digit that is a 2 or a 3.
Final answer
5416